The present invention generally relates to a compression bonding device for packaging electric components on a substrate and packaging processes therefor.
Conventionally, packaging processes for connecting electric components such as semiconductor elements to a substrate have used a compression bonding device by which the electric components are pressed against the substrate with a pressing head under heat.
Reference numeral 101 in FIG. 18(a) represents a conventional compression bonding device. The compression bonding device 101 has a pedestal 126 and a pressing head 120.
The pressing head 120 has a pressing rubber fitted into a metal frame, or a pressing rubber bonded to a metal plate with an adhesive or a liquid rubber cast into a metal frame and cured within the metal frame, etc.
In the case of a pressing rubber 122 fitted into a head body 121 made from a metal frame, the surface of the pressing rubber 122 is flush with the surface of the head body 121 or projects below the surface of the head body 121. When the pressing head 120 is pressed against an object to be pressed 110 on the pedestal 126, the surface of the pressing rubber 122 comes into contact with the object to be pressed 110.
The object to be pressed 110 has a substrate 111 and electric components 116, 118 having different thicknesses placed on the substrate 111 so that steps are formed on the substrate 111 due to the thickness differences between the electric components 116 and 118.
The pressing rubber 122 is formed of an elastic material that deforms under pressure. The pressing rubber 122 first comes into contact with the thickest electric component 116. Then, the pressing rubber 122 deforms and successively comes into contact with the electric components 116, 118 in the order of thickness from the thickest electric component 116 to thinnest electric component 118. Finally, all of the electric components 116, 118 are pressed by the pressing rubber 122.
Before the electric components 116, 118 are pressed by the compression bonding device 101, the electric components 116, 118 and the substrate 111 are aligned; and terminals of the electric components 116, 118 are directly above terminals of the substrate 111 with an adhesive 115 inserted therebetween.
The surface of the pedestal 126 is nearly horizontal, and the substrate 111 is horizontally placed on that surface. When the pressing head 120 is vertically moved downward to press the electric components 116, 118, the terminals of the electric components 116, 118 and the terminals of the substrate 111 come into contact with each other, thereby electrically connecting the electric components 116, 118 and the substrate 111 (FIG. 18(b)), because the electric components 116, 118 thrust the adhesive 115 aside and move toward the terminals of the substrate 111. Thus, the conventional compression bonding device 101 can simultaneously connect electric components having different thicknesses to one substrate.
However, if the pressing rubber 122 is depressed when it presses components 116, 118, the pressing rubber 122 has the property of bulging around the depressed part. Therefore, the bulging part of the pressing rubber 122 climbs over the frame of the head body 121 with the result that the surface of the pressing rubber 122 extends horizontally outward (FIG. 18(b)).
FIG. 19 is a plan view showing the manner in which the surface of the pressing rubber 122 extends horizontally outward, i.e., the pressing rubber 122 radially flows around the center C of its planar shape. Due to the greater amount of movement at the periphery of the pressing rubber 122 as compared with the vicinity of the center C, the electric components 116, 118 pressed by the periphery of the pressing rubber 122 horizontally move as the pressing rubber 122 extends, whereby the terminals of the electric components 116, 118 are misaligned from the location directly above the terminals of the substrate 111.
If the electric components 116, 118 are misaligned, the terminals of the electric components 116, 118 fail to come into contact with the terminals of the substrate 111, resulting in the deterioration of a reliable connection between the electric components 116, 118 and the substrate 111. See, Patent Documents No. JP A 2002-359264 and JP A 2005-32952.